The manufacture of a product typically involves a number of processing steps performed in the sequence. In most instances, these processing steps are carried out on more than one piece of processing equipment, each equipment having one or more processing chambers. For example, the manufacture of electronic devices in a wafer fabrication facility involves the performance of processing steps such as film deposition, photolithography, etching, heat treatment and dopant introduction with respect to a wafer substrate such as silicon. While it is possible to carry out some of the processing steps in a single processing equipment, it is generally the case that the substrate will have to be transferred between different processing equipments situated at different locations within the production facility.
FIG. 1 shows a known fabrication facility layout 100. The fabrication facility layout comprises a plurality of bays 120 located on opposite sides of a main bay or central isle 140. Processing equipments 150 for processing wafer substrates are arranged in a loop within a bay 120. A plurality of wafer substrates are generally grouped together and placed in a carrier such as sealed pods. The wafer substrates are then transported within the carriers between different locations in the production facility such as processing equipments 150 and storage locations. Automated transport systems such as overhead hoist transport (OHT) systems, substrate carrier handling robots, automatic or rail guided vehicles are typically employed in transporting the carriers between locations. In FIG. 1, the automated transport system comprises an OHT system including tracks 122 and 142 with a plurality of carrier transports (not shown) coupled to it. The carrier transports are adapted to transfer one or more carriers around the production facility and can take various forms such as transport vehicles that travel along the tracks 122, 142 or cradles coupled to a moving track such as a moving conveyor belt. Depending on the system, the carrier transports can be segregated into transportation that facilitate the transfer of carriers within a bay (intra-bay) versus transportation that facilitate the transfer of carriers between bays (inter-bay). Alternatively, the carrier supports can also be free to circulate freely through the fabrication facility without limitation as intra-bay or inter-bay. It is also not essential that the fabrication facility be separated into bays.
Depending upon the complexity of the electronic device, it is not uncommon for the total fabrication cycle to involve few hundred processing steps starting from a blank wafer substrate to the separation of a completed wafer into individual integrated circuits. During this time, the wafer substrates may be moved between a hundred different locations for processing, the process route possibly including a high level of reentrance in which the same processing equipment or equipment types are used. Therefore, the time taken for the transfer of wafer substrates between different locations in a fabrication facility including time spent waiting for a carrier transport to pick up the carrier within which the substrates are placed plays an important role in determining the total elapsed time for making an electronic device also known as fabrication cycle time.
In today's semiconductor industry, manufacturers are trying to improve their market share by improving wafer yield and providing shorter cycle time to attract more customers. Therefore, efficient manufacturing automation systems and methods for transferring work in progress materials such as wafer substrates in a fabrication facility are desirable.